The document FR2595972 discloses a percussion apparatus, including:                a body delimiting a piston cylinder,        a striking piston alternately movable inside the piston cylinder, and arranged to strike a tool during each operating cycle of the percussion apparatus,        a control distributor arranged to control a reciprocating movement of the striking piston inside the piston cylinder reciprocally along a striking stroke and a return stroke,        a control device arranged to vary the striking stroke of the striking piston depending on the hardness of the ground encountered by the tool, the control device comprising:        a control cylinder,        a plurality of control channels each opening into the control cylinder, each control channel also opening into the piston cylinder and being adapted to be put in communication with a high-pressure fluid supply circuit during at least one part of the reciprocating movement of the striking piston,        a control channel connected to the control distributor and opening into the control cylinder,        a control slide movably mounted in the control cylinder between a plurality of control positions in each of which the control slide is configured to fluidly connect the control channel with at least one of the control channels,        a first control chamber delimited by the control slide and the control cylinder, a first face of the control slide being located in the first control chamber, and        a second control chamber delimited by the control slide and the control cylinder and permanently connected to a low-pressure return circuit, a second face of the control slide, opposite to the first face, being located in the second control chamber.        
The control device further comprises a flow regulating member, formed by a volumetric pump, actuated in synchronisation with the striking piston. The flow regulating member is shaped to ensure the intake, at each operating cycle of the percussion apparatus, of a predetermined amount of fluid in the first control chamber.
The control device also comprises a discharge channel opening respectively into the piston cylinder and into the first control chamber, the discharge channel being configured to be put in communication with the low-pressure return circuit, via a peripheral groove provided on the striking piston and a connecting channel permanently connected to the low-pressure return circuit and opening into the piston cylinder, when the striking piston is in and/or close to a theoretical striking position.
The discharge channel is configured to discharge, at each operating cycle of the percussion apparatus, an amount of fluid out of the first control chamber, which depends on the residence time of the striking piston in and/or close to the theoretical striking position thereof and therefore on the hardness of the ground encountered by the tool. These dispositions allow adjusting the position of the control slide and accordingly the length of the striking stroke of the striking piston depending on the hardness of the ground encountered by the tool.
A drawback of such a percussion apparatus lies in the complexity of the production of the volumetric pump. Indeed, such a volumetric pump requires the production of rectified slides and bores, implanted in one or more heavy and expensive part(s).
The present invention aims to overcome these drawbacks.